System for a plurality of video cameras disposed on a common network
View Patent ↗A plurality of cameras are adapted to utilize Ethernet network protocol for the physical layer and UDP/IP for the network and transport layers permitting multiple compressed signals representing different degrees of image resolution, compression type of compressed bit rate to be simultaneously transmitted. These multiple video streams may be combined into one composite stream for network transmission or may be maintained as separate and distinct video or still frame streams throughout the network. The digitizer, compressor and network interface can be integral to a camera or can be a separate unit. Video or images networked in this manner may be selective viewed on an operator console or may be received by a network server for storage, analysis and subsequent retrieval.
1. A surveillance system having a plurality of video cameras disposed on an Ethernet network and adapted for communicating with the ethernet network, the system comprising:
a plurality of cameras;
a digitizer of each camera, the digitizer being integral in a common housing with the respective camera;
a network interface for each camera, the network interface being integral in a common housing with the respective camera, the network interface being connected to the ethernet network;
each camera communicating with the ethernet network through the network interface;
a plurality of compressors integral in a common housing with each camera in advance of the network interface at each camera, each of the compressors outputting a respective compressed signal, the compressed signals each having at least one characteristic different from other of the compressed signals, the at least one characteristic being selected from among:
image resolution, compression type and compressed bit rate;
the network interface including an IP network stack, the IP network stack being configured to provide a plurality of IP data packets, the plurality of IP data packets conveying the compressed signals;
the camera including memory and a processor associated with the memory;
the camera including timestamp application software stored in the memory and executable upon operation of the processor, the timestamp application software when executed attaching presentation timestamps (PTS's) in I-frame packets of the compressed signals;
a receiver adapted to be connected to the ethernet network to receive the compressed signals at a location remote from the camera, the receiver including:
memory;
a buffering software application stored in memory, the buffering software application including executable steps prescribing:
extracting presentation timestamps (PTS's) from each of a series of received I-frame packets;
adding to extracted presentation timestamps (PTS's) a time offset sufficient to account for worst case network delay, the extracted presentation timestamps (PTS's) and time offset when added providing a series of respective sums;
a video player software application stored in memory, the video player software application when executed playing received compressed signals in series in relation to the sums;
a processor in communication with memory, the processor being operable to execute the executable steps; and
the receiver further including
the video player software application including a video player time base,
the video player time base providing a measure for pacing play of the received compressed signals;
the buffering software application including executable steps prescribing:
the time offset being a predicted delay value (delta T), the predicted delay value (delta T) initially being an estimate of worst case network delay, the extracted presentation timestamps (PTS's) and predicted delay value (delta T) when added providing the series of respective sums;
substituting the respective sums for each presentation timestamp (PTS) to delay playback of each frame by the predicted delay value (delta T);
obtaining a local prediction of delay (local delta T) from the video player time base;
changing the predicted delay value (delta T) by a difference amount, the difference amount being calculated between the predicted delay value (delta T) and the local prediction of delay (local delta T) before adding the predicted delay value (delta T) to a next extracted presentation timestamp (PTS's) extracted from the series of received I-frame packets.